[HN Gopher] USB MIDI interface for the NeXTCube - ISPW board
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       USB MIDI interface for the NeXTCube - ISPW board
        
       Author : zdw
       Score  : 57 points
       Date   : 2023-05-16 23:02 UTC (23 hours ago)
        
 (HTM) web link (0110.be)
 (TXT) w3m dump (0110.be)
        
       | dfox wrote:
       | One thing that this article mentions is that MIDI is a interface
       | that is inherently optically coupled. The notionally differential
       | wires end up in the LED inside of an optocoupler. Reason for that
       | design is a general aversion of audio people to anything that
       | might cause what they call "ground loop".
       | 
       | And then well, in 21st century there are various half-assed
       | implementations of the MIDI physical layer (mostly assuming that
       | it is essentially a TTL) that end up non-working and non-working
       | because of the ridiculous currents that flow through the cable
       | that shorts ground of one device to the power bus of another.
        
         | jalk wrote:
         | Here is a snip from the midi specification
         | 
         | > The MIDI circuit is a 5mA current loop; logical 0 is current
         | ON.... To avoid ground loops, and subsequent data errors, the
         | transmitter circuitry and receiver circuitry are internally
         | separated by an opto-isolator
         | 
         | Ground loops is not something the audiophools have cooked up.
         | Ethernet devices are also isolated from each other, although it
         | uses 1:1 transformers (Ethernet Magnetics) instead of
         | optocouplers.
         | 
         | The optocoupler also works like a cheap (although somewhat hard
         | to replace) fuse which is probably a good thing if you want to
         | connect you Roland Jupiter-8 / Fairlight CMI to some dodgy
         | equipment.
        
           | zdw wrote:
           | > Ethernet devices are also isolated from each other,
           | although it uses 1:1 transformers (Ethernet Magnetics)
           | instead of optocouplers.
           | 
           | Unless you're using fiber as your medium, but that's an
           | optocoupler by definition...
        
         | pantulis wrote:
         | I swear I have _heard_ sysex dumps on my speakers, specially
         | using older serial "To-Host" cables.
        
         | boffinAudio wrote:
         | You have to try pretty hard to mess up MIDI, hardware-interface
         | wise. Its one of the most widely understood and implemented
         | serial protocols out there ..
        
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       (page generated 2023-05-17 23:01 UTC)